Conversion of hydrocarbons



Patented Mar. 10, 1942 CONVERSION OF HYDROCARBONS Elmer R. Kanhofer, Chicago, Ill., assignor to Universal Oil Products Company, Chicago, 111., a

corporation of Delaware No Drawing. Application June 30, 1939, Serial No. 282,067

6 Claims.

This invention relates to the conversion of mixtures of hydrocarbons comprising olefin-containtion so that a gasoline saturated in respect to the bromine number and consisting essentially only of parafiln and aromatic hydrocarbons is produced.

Cracked gasolines produced either by strictly thermal or thermal-catalytic processes contain varying percentages of olefinic hydrocarbons depending upon the type of stock cracked and the severity of the cracking conditions employed, high with suitably chosen catalysts under the conditions specified that a number of simultaneous and concurrent reactions occur among the hydrocarbons so that not only are the olefins present in the cracked gasoline hydrogenated to produce the corresponding paraflins, but that the olefins in the gasoline produced by the cracking of the gas oil are also hydrogenated. Apparently some saturated constituents of the gas -oils employed, probably naphthenes, undergo dehydrogenation to furnish hydrogen for the hydrogenation of the olefins to produce par'afiins therefrom, thus producing on the one hand aromatics from the naphthenes and parafiins from the olefins, the blend of these two types of hydrocarbons having relatively high antiknock value and at the same time beingfree from olefinic'and similarly reactive hydrocarbons. While not limiting the invention to the theory expressed, the following equation may be suggested as explaining the mechanism of the reaction.

temperatures'and low pressure having a tendency to produce relatively higher percentages of olefins. While such gasolines, particularly when stabilized against deterioration by the use of inhibitors, are entirely suitable for use in ordinary automobile engines, the. requirements for fuels to be used in high compression airplane engines are much more severe since the slightest tendency. toward gum formation or plugging of feed lines must be eliminated, while at the same time, the antiknock value must be high to insure maximum power output from the motors. These rigid requirements are met substantially only by isoparaflmic hydrocarbons and some aromatics and naphthenes which have low enough meltingpoints either alone or in admixture with other hydrocarbons to prevent freezing at the low tem peratures encountered at high altitudes. It is a particular object of the present invention to provide a process for producing substantially saturated high antiknock value motor fuels suitable for use in airplane engines.

In one specific embodiment, the present invention comprises the treatment of mixtures of cracked gasolin-es and distillate fractions of the nature of kerosene or gas oil by contacting saidmixtures with granular catalytic material formed .by calcining an alkali metal-free composite of Cyclohexane Hexene Benzene Horace more complex reactions involving the splitting of carbon-to-carbon bonds, isomerization, recombination of radicals, etc. In the equation, cyclohexane typifies naphthene hydrocarbons present in kerosenes or gas oils While the hexene typifies an olefinic constituent of a low boiling distillate of the nature of gasoline. While test work has indicated that the hydrogen for the saturation of the olefins comes principally from the naphthenic constituents of the gas oil and similar fractions, some hydrogen is undoubtedly gained from the dehydrogenation and cycling of various parafi'inic constituents originally present and from the further dehydrogenation of the cyclic compounds produced. The overall effect uniformly observed, however, is that the gasolines produced by treating hydrocarbon mixtures of the type described consist predominantly of paraflinic and aromatic hydrocarbons, as indicated by relatively low bromine numbers as will be brought out in a subsequent section devoted to numerical data;

The process requires a relatively active catalytic material to be presently described, the use of temperatures materially below the ordinary cracking range of either strictly thermal or thermal-catalytic processes and moderately long times of contact with the catalyst. The reactions are further favored by increased pressure which assists the secondary hydrogenation reactions;

The catalystswhich are preferred for use in the present processare of a very specific character and require the use of an exact method of preparation.

According to the description of the preparation of the preferred catalysts given below, precipitated alumina hydrogel and/or zirconia hydrogel are composited with silica hydrogel, and then the composite is washed, dried, formed into particles, and calcined to produce a catalytic mass. However, the different catalysts which may be so produced do not necessarily give equivalent results.

In the following specification the terms silicaalumina, silica-zirconia, and silica-alumina-zirconia masses are used in a broad sense. Inasmuch as the chemical knowledge of the solid state has not been developed perfectly, it is not possible to give the structure of all solid substances. All that can be said definitely concerning these masses is that they contain silicon, oxygen, alu- 'minum, and/or zirconium. Generally speaking,

however, all these components show more or less low catalytic activity individually but in th aggregate display high activity This activity is not an additive function, it being relatively constant for a wide range of proportions of the components, whether in molecular or fractions of molecular proportions. No one component can be determined as the one component for which the remaining components may be considered as the promoters according to conventional terminology, nor can any components be determined as the support and the others the catalyst proper.

In manufacturing the preferred catalysts in accordance with the present process it is necessary to employ silicawhich has been prepared by precipitation from solution as a hydrogel within or upon which the alumina and/or zirconia are deposited also by precipitation as hydrogels. The most convenient and ordinary method of preparation of a satisfactory silica gel is to acidify an aqueous solution of sodium silicate by the addition of the required amount of hydrochloric acid. The excess of acid and the concentration of the solution-in which the precipitation is brought about will determine the eventual primary activity of the silica and its suitability for compositing with the alumina and/or zirconia hydrogels to produce a catalyst of high activity. In general, the most active silica is produced by adding only enough acid to cause gel formation to occur 'in the sodium silicate, but the material formed at such a point is rather gelatinous and is filtered with difliculty. Further the silica hydrogel is coagulated incompletely at this point. By adding a moderate excess of acid after the hydrogel has formed, the more desirable physical characteristics in regard to catalyst activity are conserved while the filtrability is generally improved and the silica hydrogel is precipitated more completely. Fairly good hydrated silica for present catalytic purposes may be made by employing as highas a excess of hydrochloric acid, but'beyond this point the more desirable properties are lost. After precipitating the silica gel it is preferably washed until substantially free from salts by using several alternative reagents, which will be described later.

In one mode of preparing the activated form, the silica hydrogel may be boiled either with separately precipitated aluminum hydroxide and/or zirconium hydroxide gel, which is added in the wet condition to the silica/suspension, or th silica hydrogel may be suspended in and boiled within an aluminum chloride or the silica gel may be treated similarly by an aqueous solution containing both aluminum and zirconium salts. In either case the final precipitate comprising essentially the hydrated silica and hydrafted alumina and/or zirconia is finally washed to substantially complete removal of water soluble materials and dried at about 300 F. to produce a rather crumbly and granular material which may be ground and pelleted or sized to produce particles of catalyst. Since this material is calcined at a temperature in the approximate range of 1000-1500 F. and is used at a temperature of the order of 500-900 F. its water content sulfide to aqueous solutions of aluminum and/or zirconium salts, followed by suitable washing to remove impurities. The alumina and/or zirconia hydrogels may be precipitated from such solution inwhich previously prepared and washed hydrated silica is suspended, followed by a washing of the-total composite precipitate. Similarly, purified silica may be suspended in a solution of an aluminate, such as sodium aluminate and alumina precipitated by the addition of the aluminum salts or by the requisite quantities of acid. As a "further alternative method of producing the desired catalysts, aluminum and/or zirconium salts may be added to a solution of an alkali metal silicate to jointly precipitate silica hydrogel with the hydrogels of alumina and/or zirconia and further amounts of silica hydrogel may then be precipitated by the addition of acid. A characteristic equation illustrating the preparation of a silica-alumina catalyst is given below, although in it no account is taken of water of hydration:

It will be obvious that the employment of the reaction shown in the above equation will be limited on account of the molal proportions involved so that such a method of preparation of a composite may need supplementing by the presence or further precipitation of silica to obtain the desired ratio.

A specific and satisfactory method of preparing silica-alumina catalysts used in accordance with the present invention is given below, although not with the intention of unduly limiting the proper scope of the invention. By following the procedure outlined with a suitable choice of reagents of accepted purity, good catalysts for nearly all cracking reaction may be produced.

In the finished catalysts, prepared as indicated above, the weight ratio of silica to alumina and/or zirconia may vary within a considerable range, for example from 30 to 0.1, although as a rule catalyst composites having optimum activity basedon yields'and quality of gasoline produced will correspond to silica-oxide weight ratios of theorder of about 30 to 10 in which the term oxide is used in reference to alumina and/or zirconia. These proportions will vary considerably with the particular fractions subjected to treatment and the degree of conversion found to be optimum in any particular case.

It is to be recognized that very little is known positively. concerning the mechanism of enhanced activity of complex catalysts and no attempt will be made herein to offer any definite reasons for the observed mutually promotional effect of silica with alumina and/or zirconia composites prepared for catalytic purposes according to the present invention. There may be a catalytic effect due to the juxtaposition of the catalyst components and it may be that the oxide (alumina and/or zirconia) is the more active catalyst and is extensively dispersed in and on the silica in order to present a large surface.

The following numerical data is given in support of the value of the present process although not with the intention of imposing undue limitations on the proper scope of the invention.

Blends were made of a gasoline produced by thermally cracking an East Texas gas oil and further quantities of the gas oil itself. These blends were passed through a silica-aluminazirconia composite catalyst under conditions indicated in the appended table. The catalyst was prepared by the general procedure outlined in the preceding specification and consisted of approximately 100 molar proportions of silica, 2 molar proportions of alumina, and 4 molar proportions of zirconia. In the table, A refers to the-cracked gasoline, and B to the gas oil.

Run N o.

40% A 75% A Charge 60% B 25% B Space velocity, liquid. 1. 1.0 Temperature .F 800 700 Pressure "lbs/sq. in. 0.0 100 Yields:

Total liquid "percent by vol 85 90 Loss as gas and heavy material 15 10 Bromine Nos. (300 F., E. P.):

Charge 75 72 1st t hr. cut 23 0. 56

37. 5 72. 0 70.0 90.0 55.0 81. 5 52.0 78.0 4th M hr. cut 52.0 76. 0 Inspection of 300 F., E. P. gasoline in ch gc:

Octane number, motor method 71. 0 71. 0 Octane number, after addn. of 6 cc. tetraethyl lead 81. 5 81. 5 Inspection of gasoline product:

Cuts included 1 and 2 l and 2 End point 400 300 Octane number, motor method. 72 68 Octane number+3 cc. tetraethyl lead 83. 5 Octane number+6 cc. tetraethyl load 90. 5

It will be seen from the above table that in about the first hour of operation in the runs made either at 800 or 700 F. that the bromine numbers were very low on the material boiling below 300 F. It will also be seen that the yield of this material was very high for the first hour although the yield in the second half hour was somewhat lower than the yield in the first half hour.

It is further seen that the 400 F. endpoint material in the products from run No. 1 and particularly the 300 F. endpoint material from the products of run No. 2 at the lower temperature had a considerably increased susceptibility to the action of tetraethyl lead. In the place of the last mentioned 300 F. endpoint material, the octane number was three points lower than the corresponding material in the charge, but was nine points higher when the same amount of tetraethyl lead was added. The low bromine numbers indicate substantially complete saturation and absorption of material amounts of olefins or diolefins, either of a straight chain or cyclic character.

It is obvious from'the above that the best results in the present type of process are obtainable with short periods of operation with a relatively fresh and active catalyst. These conditions are met by running for short periods and then reactivating by burning oflf traces ofcarbonaceous deposits and this feature is comprised within the scope of the present invention.

I claim as my invention:

1. A process for producing motor fuel of high anti-knock value and relatively low olefin content which comprises combining olefinic gasoline with a hydrocarbon oil heavier than gasoline and containing a substantial proportion of saturated hydrocarbons, and subjecting the resultant mixture to the action of a catalyst comprising a calcined mixture of precipitated silica hydrogel and precipitated alumina hydrogel at a temperature in the approximate range of 500- 800 F. for a contact time sufficient to convert a substantial portion of said heavier oil into gasoline and to efiect substantial saturation of gasoline boiling olefins.

2. A process for producing motor fuel of high anti-knock Value and relatively low olefin content which comprises combining olefinic gasoline with a hydrocarbon oil heavier than gasoline and containing a substantial proportion of saturated hydrocarbons, and subjecting the resultant mixture to the action of a catalyst comprising a calcined mixture of precipitated silica hydrogel and precipitated zirconia hydrogel at a temperature in the approximate range of SOD-800 F. for a contact time sufficient to convert a substantial portion of said heavier oil into gasoline and to efiect substantial saturation of gasoline boiling 4. The process as defined in claim 1 further.

characterized in that said hydrocarbon oil is a straight run naphthenic petroleum fraction.

5. The process as defined in claim 2 further characterized in that said hydrocarbon oilis a straight run naphthenic petroleum fraction.

6. The process as defined in claim 3 further characterized in that said hydrocarbon oil is a straight run naphthenic petroleum fraction.

ELMER R. KANHOFER. 

